Sheep in the uplands of the United Kingdom face a series of choices as to where to graze. These choices have been shown to be influenced by the spatial distribution of nutrient supply from herbage (Duncan et al., 1994). Micro-climatic variation may also determine where animals forage, particularly in topographically complex environments found in upland areas. Wind and rain have marked effects on heat loss and hence on lower critical temperature (LCT) in sheep (Blaxter, 1977). Mount and Brown (1982) demonstrated that there were occasions during a year when sheep were below their LCT. This study assumed that data gathered from a standard meteorological station were applicable to conditions actually experienced by grazing animals and took no account of the ability of herbivores to select a more favourable micro-climate under extreme conditions (Mount and Brown, 1982). The experiment reported here was carried out to examine the extent to which microclimate influenced the distribution of grazing by sheep under windy conditions. Micro-climate was manipulated using artificial shelters.